1. Field of the Invention
This invention relates to a protecting device for car air conditioners suitable for protection of compressors of the car air conditioners or more specifically, for control of an electromagnetic clutch transferring rotation of an engine to the compressor.
2. Description of the Prior Art
In car air conditioners, rotation of an engine is usually utilized to rotate a compressor compressing a refrigerant. An electromagnetic clutch is provided on a rotational shaft at the compressor side to drive and stop the compressor. More specifically, a transmission belt is provided between a pulley mounted on a rotational shaft of the engine and another pulley rotatably mounted on the rotational shaft at the compressor side. The electromagnetic clutch is provided between the pulley at the compressor side and a rotor shaft of the compressor. A control signal is delivered to make and cut off a current supply path to the electromagnetic clutch so that the car air conditioner is controlled. The transmission belt is also used to drive pulleys for auxiliary equipment such as an alternator and/or hydraulic booster.
In the above-described car air conditioner, the compressor is continuously engaged via the transmission belt with the engine unless a manually switch is operated to turn off the electromagnetic clutch. Accordingly, when the compressor fails into a non-rotatable state for some reason or other, the transmission belt slips between the pulleys. The slip causes friction and heat which cut off the transmission belt. Consequently, the auxiliary equipments linked to the engine become inoperative. This may result in a hazardous condition in the driving of a car, or the car may be incapable of traveling. In view of the problem, the prior art has recently proposed a protecting device in which the rotation of the compressor is detected to thereby detect the unrotatable state thereof and the slip of the transmission belt so that the current supply path for the electromagnetic clutch is automatically cut off on the basis of the results of detection for escape from danger.
FIG. 18 illustrates such a conventional protecting device for car air conditioner. As shown, an engine room and a compartment are divided by a partition wall 107. A main body of the protecting device 101 is disposed near a console inside the right-hand compartment. At least one end of each of control signal wires 102 and an electric supply wire 103 are connected to the protecting device 101. The other electric supply wire (not shown) is grounded through the metal car body. The other end of each of the signal wires 102 is connected to a rotation sensor 105 mounted on a compressor 104 of the car air conditioner. The electric supply wire 103 is connected to an electromagnetic clutch 106 so that the same is driven. A connector 108 is provided for connecting these wires. The protecting device 101 is connected via a power switch SW for the car air conditioner to a power source.
In the above-described protecting device 101, the electromagnetic clutch 106 is energized through the electric supply wire 103 upon turn-on of the air conditioner power switch SW so that a pulley 109 is directly connected to the compressor 104 by the electromagnetic clutch 106. The protecting device 101 detects a signal delivered from the rotation sensor 105 mounted on the compressor 104 to thereby judge a rotational speed of the compressor. When the compressor 104 is in a non-rotatable state on the basis of the intervals of output signals or when the rotational speed of the compressor is at or below a predetermined value, the electromagnetic clutch 106 is immediately deenergized so that the transmission belt is unburdened for the prevention of fracture thereof and an adverse effect on the auxiliary equipment.
The protecting device 101 is disposed in the car compartment on the right of the partition wall 107, whereas the rotation sensor 105 is mounted on the compressor 104 disposed in the engine room on the left of the partition wall 107, as viewed in FIG. 18. Accordingly, the signal wires 102 and the electric supply wire 103 need to be drawn from the engine room into the car compartment. This results in a complicated wiring work. Furthermore, an external noise tends to be superposed on the signal from the rotation sensor 105 since the signal wire 102 is long. Particularly, the rotation sensor 105 has recently been proposed to be rendered smaller in size and composed of more semiconductor components. These reduces the magnitude of the output signal delivered from the rotation sensor 105. Consequently, there is a higher possibility of malfunction of the protecting device. Additionally, the connector 108 for the three wires and wiring for the long signal wires result in an increase in the costs of the protecting device. A cost decrease is accordingly desired.